Role of vitamin E-coated membrane in reducing advanced glycation end products in hemodialysis patients: a pilot study.

INTRODUCTION: Advanced glycation end products (AGEs) are markers of oxidative stress. AIMS: To assess if a vitamin-E-coated dialyzer affects plasma AGE levels and endothelial function in hemodialysis patients. METHODS: 16 patients were dialyzed with a synthetic modified cellulose membrane (SMC, n = 8) or a vitamin E-coated dialyzer (n = 8), respectively. At week 32 endothelial function was determined as brachial artery flow-mediated dilatation (FMD). Total AGEs, free pentosidine (FP), protein-bound pentosidine (BP) and autoantibodies against oxidized LDL (ox-LDL-autoantibodies) were assessed at baseline (T0) and at 16, 32, 40 and 42 weeks (T16, T32, T40 and T42). RESULTS: At T16 and T32 FP and BP were lower in vitamin E than in SMC (T 16: 88.7 +/- 8.96 vs. 124.2 +/- 11.90 pmol/ml plasma; p = 0.04, and 22.9 +/- 2.99 vs. 32.8 +/- 2.98 pmol/mg proteins; p = 0.04. T32: 78.7 +/- 8.54 vs. 123.7 +/- 10.15 pmol/ml plasma; p = 0.007, and 19.9 +/- 2.0 vs. 33.67 +/- 2.41 pmol/mg proteins; p = 0.001). In vitamin E, AGEs were lower at T32, T40 and T42 (946.7 +/- 80.91 vs. 1,351.2 +/- 179.33 AU/ml, p = 0.05; 986.9 +/- 59.63 vs. 1,509.9 +/- 154.17 AU/ml, p = 0.013; 890.3 +/- 73.70 vs. 1,453.9 +/- 153.16 AU/ml, p = 0.009). At T32 AGEs, ox-LDL autoantibodies and FMD were inversely correlated (R = -0.70 p = 0.007 and R = -0.59, p = 0.04, respectively). CONCLUSIONS: Vit E-coated membrane reduces plasma AGEs levels and AGEs values are negatively correlated with FMD.

Triglyceride-rich lipoproteins from hypertriglyceridemic subjects induce a pro-inflammatory response in the endothelium: Molecular mechanisms and gene expression studies.

Triglyceride-rich lipoproteins (TGRLs) are a cardiovascular risk factor and induce endothelial dysfunction. In the present study we investigated the effects of TGRLs from type IV hyperlipidemic and normolipidemic subjects on endothelial activation focusing on the effects on intracellular pathways and gene expression. A total of 54 subjects, 30 hypertriglyceridemic (triglyceride (TG) levels 284+/-101 mg/dl) and 23 normotriglyceridemic (TG levels 109+/-40 mg/dl) were enrolled as lipoprotein donors. TGRLs were isolated from hypertriglyceridemic (H-TGRL) and normotriglyceridemic (N-TGRL) subjects. RNA from human endothelial cells incubated with N-TGRL or H-TGRL was prepared for cDNA microarray analyses. Western blotting was used to study intracellular signaling pathways. Regulated genes were further studied with real-time PCR, immunofluorescence and FACS. Furthermore, a protein/DNA array and chromatin-immunoprecipitation were used to identify transcription factors involved in the observed effects. Both N-TGRL and H-TGRL activated ERK1/2 and p38 MAPK. However, there were differences in the pattern of upregulated target genes between the two types of lipoproteins in HUVECs and/or HAECs: PAI-1, VCAM-1, ELAM-1 and MCP-1 were upregulated by both N-TGRL and H-TGRL, while PECAM-1, IL-6 and ADAMTs1 were selectively upregulated by H-TGRL. Chromatin immunoprecipitation analysis demonstrated the involvement of transcription factors NF-kB and CREB in the activation of these genes. These results support the possible involvement of hypertriglyceridemic TGRLs in endothelial dysfunction via induction of a pro-inflammatory and pro-thrombotic state.

Effect of the Toll-like receptor 4 (TLR-4) variants on intima-media thickness and monocyte-derived macrophage response to LPS.

OBJECTIVES: Toll-like receptor 4 (TLR-4) is believed to contribute to the initiation and progression of atherosclerosis. The association of the D299G polymorphism of the TLR-4 gene with the progression of coronary and carotid atherosclerosis, risk of cardiovascular events and myocardial infarction is controversial. We have investigated whether the presence of the D299G polymorphism and the co-segregated T399I polymorphism affects the intima-media thickness (IMT) in the general population. SUBJECTS: The PLIC study population (n = 1256) was genotyped for the D299G and the T399I polymorphisms. RESULTS: The presence of both the D299G and T399I alleles was observed in the 13.0% of the population, carriers of the T399I alone were 1.8% and of the D299G alone were 0.9%. No difference in IMT was detected within the carriers of the D299G and T399I alleles and the wild-type subjects in the PLIC population. Furthermore, we investigated whether monocyte from D299G to T399I subjects present a defective response to CD40, interleukin (IL)-6, monocyte chemotactic protein (MCP)-1, cyclo-oxygenase (COX)-2 and PTX3 expression induced by lipopolysaccharide (LPS). When the monocyte-derived macrophages of these subjects were challenged with LPS (1 mug mL(-1)), no impact of the polymorphisms on the induction of CD40, MCP-1 and PTX3 was observed. Only IL-6 and COX-2 induction by LPS resulted reduced in the D299G/T399I carriers. CONCLUSION: The presence of the D299G and T399I polymorphisms of the TLR-4 gene does not play a major role on the progression of carotid atherosclerosis. Macrophages from the subjects carrying the polymorphisms show an impaired response to LPS limited only to a IL-6 and COX-2.

Acute effect of high-fat meal on endothelial function in moderately dyslipidemic subjects.

OBJECTIVE: Hypercholesterolemia markedly impairs endothelial function. Whether this is the case for hypertriglyceridemia is less clear, however, and limited evidence exists on the effect of an acute increase in triglyceridemia caused by a high-fat meal. METHODS AND RESULTS: In 16 normotensive subjects with an untreated mild hypertriglyceridemia and dyslipidemia and in 7 normal controls, we measured radial artery diameter and blood flow by an echo-tracking device (NIUS02). Data were obtained at baseline, at the release of a 4-minute ischemia of the hand, which causes an increase in arterial diameter dependent on nitric oxide (NO) secretion, and at the release of a 12-minute exclusion of the arm by an arm cuff to obtain a larger increase in arterial diameter mainly of nonendothelial nature. Measurements were performed before and 6 hours after a high-fat meal (680 kcal/m(2) body surface; 82% lipids). In mild dyslipidemic hypertriglyceridemic subjects, the high-fat meal did not alter baseline blood pressure (beat-to-beat finger measurement), heart rate, radial artery diameter, and blood flow. It also did not alter the increase in blood flow induced by the 4-minute ischemia (+42.7+/-10.4 and +43.7+/-10.4 mL/min), whereas it markedly attenuated the concomitant increase in arterial diameter (+0.31+/-0.06 versus 0.13+/-0.06 mm; P<0.05). The alteration of the diameter response did not correlate with changes in total cholesterol, but it showed a significant correlation with the increase in serum triglycerides induced by high-fat meal (r=0.49, P<0.05). This attenuation was not seen in control subjects and in subjects in whom measurements were repeated after a 6-hour observation period. It was also not paralleled by an alteration of the endothelially independent response to a 12-minute ischemia whose larger effects on arterial diameter and blood flow were similar before and after the high-fat meal. CONCLUSIONS: Endothelial function is markedly impaired by a high-fat meal that causes an acute hypertriglyceridemia. This impairment is evident in dyslipidemic patients with baseline hypertriglyceridemia but not in normotriglyceridemic controls. An oral fat load was administered to 55 HIV-positive and 10 HIV-negative individuals. Postprandial clearance of triglyceride-rich lipoproteins was delayed in HIV-positive individuals. Compared with HIV-positive subjects not on PIs, those taking PIs do not have increased postprandial triglyceride-rich lipoproteins but do have increased postprandial intermediate-density and low-density lipoproteins. Hypercholesterolemia impairs endothelial function, whereas the effect of hypertriglyceridemia is less clear. In normotensive subjects with an untreated hypertriglyceridemia and hypercholesterolemia, we measured endothelial function before and 6 hours after a high-fat meal. The results demonstrate that in moderately dyslipidemic patients, endothelial function is impaired by acute hypertriglyceridemia.

Low density lipoprotein oxidation, antioxidants, and atherosclerosis.

Oxidized low density lipoproteins (LDLs) are believed to be the most atherogenic form of LDL. However, although a number of experimental data support this concept, the protective role of antioxidants that may prevent LDL oxidation in atherosclerosis is only partially confirmed by studies in humans. Observational and epidemiologic data as well as randomized trials failed to provide clear-cut indications because of mixed results on the protective role of antioxidants against cardiovascular diseases. In spite of the lack of a general consensus, recent data reinforce the concept that a regular intake of antioxidants present in food blocks the progression of atherosclerosis and that the reduced oxidisability of LDL may represent a good marker to follow the action of antioxidants. When it becomes possible to monitor the efficacy of any antioxidant therapy with validated markers of oxidation, the potential influence of vitamins and antioxidants on coronary artery disease will eventually be resolved.

A successful dietary treatment fails to normalize plasma triglyceride postprandial response in type IV patients.

The role of plasma triglycerides as a risk factor for cardiovascular disease is still under scrutiny. While recent studies have shown that postprandial triglyceridemia is an independent risk factor, normalization of fasting plasma triglycerides through modification of nutritional habits remains the primary approach in the treatment of hypertriglyceridemia. To address the issue of whether a satisfactory dietary regimen results in the control of postprandial lipemia, 53 type IV hypertriglyceridemic patients underwent an hypolipidemic diet for 3 months. All patients had a reduction of fasting lipid parameters (average TG: from 516+/-208 to 229+/-99 mg/dl; total cholesterol (Chol): from 261+/-42 to 213+/-40 mg/dl and HDL Chol: from 33+/-9 to 38+/-8 mg/dl). Taking plasma TG < or =200 mg/dl as the target for dietary intervention 26 patients were classified as 'responders' while the remaining 27 were 'non responders'. Even if fasting total TG, total Chol, HDL and LDL Chol were normal, both responders and non responders (P<0.0001) showed an exaggerated postprandial response to an oral fat load as compared to controls (20 normolipidemic subjects). Also when 10 responders and 10 controls, all male, were matched for plasma TG (129+/-43 versus 121+/-41 mg/dl) and other lipid parameters, a statistically significant difference between the two groups was observed at the time of each of the postprandial tests (P<0.0001) and for the area under the curve. The fact that the post prandial response is poorly modified by a dietary regimen, that effectively reduces plasma fasting TG, suggests that commonly used dietary regimens fail to restore a normal postprandial metabolism. Whether the cardiovascular risk for these patients is reduced after diet remains, therefore, to be addressed.

SIM 6080, a new calcium antagonist, reduces aortic atherosclerosis in cholesterol-fed rabbits.

SIM 6080 is a new calcium antagonist, structurally related to diphenylalkylamines, which combines transmembrane and intracellular calcium antagonist activities. In the present study we investigated the effect of SIM 6080 on atherogenesis in cholesterol-fed rabbits. Subcutaneous administration of the compound at 0.33, 1, and 3 mg kg-1/bid for 60 days neither affected plasma lipids nor blood pressure. However at 1 and 3 mg kg-1/bid SIM 6080 reduced in a dose-dependent manner both the area of the aorta covered by plaques and aortic cholesterol content. Determination of SIM 6080 plasma and aortic content indicated that the compound could concentrate up to 10 times in the arterial tissue. In vitro studies demonstrated that at concentrations similar to those observed in the aorta this compound may stimulate rabbit beta VLDL catabolism by smooth muscle cells in an homologous system suggesting that the up-regulation of LDL-receptors in the aorta may contribute to the antiatherosclerotic properties of SIM 6080.

Characterization of a family with moderate hypercholesterolemia and binding defective low density lipoprotein.

Familial defective apolipoprotein B-100 (FDB) is a genetic disorder presenting with hypercholesterolemia and abnormal low density lipoprotein (LDL) that binds poorly to LDL receptors. This disease appears to be caused by a mutation in the apo B gene. In the present study thirteen members of a family with moderate hypercholesterolemia (250-350 mg/dl) were investigated. Biochemical studies on cultured skin fibroblasts ruled out classical familial hypercholesterolemia (receptor deficiency). LDL from nine affected members displayed, in an "in vitro" cell binding assay, a reduced affinity (2.5 fold) for the receptor, and had normal electrophoretic mobility, size and chemical composition. Lp(a) levels in family members were comparable to those present in normolipidemics and lower than those observed in primary hypercholesterolemia. The disorder is transmitted over three generations as an autosomal codominant trait and all the affected members are heterozygotes and hypercholesterolemic.

Ability of the LDL receptor from several animal species to recognize the human apo B binding domain: studies with LDL from familial defective apo B-100.

To verify whether the LDL receptors from different animal species recognize the binding domain of human apo B-100 we studied the interaction of LDL from control and familial binding defective apo B-100 (FDB) with cultured cells. Human, monkey, bovine, guinea pig and rabbit LDL receptors distinguish between normal and binding defective LDL with a displacement ratio (defective/normal) of 3.3, 2.6, 3.4, 3.1 and 2.0, respectively. Guinea pig and rabbit receptors, however, showed affinities 2-3-fold lower than the human receptor. Hamster, rat and mouse cells failed to differentiate between normal and FDB LDL with a ratio of 1.2, 0.8, and 1.4; the apparent affinities were 4-8 times lower than that of the human receptor. The data from the latter species suggest that the LDL receptor recognizes an area of human apo B different from the human receptor binding domain. The ability of antibody Mb47 to inhibit the binding of human LDL to human, rabbit and guinea pig but not to mouse cells further stresses this concept. Moreover, in 17 alpha-ethinyl estradiol-treated rats the rate of disappearance from plasma of FDB and control 125I-labelled LDL was identical, thus confirming the in vitro observations. These data suggest that the binding domain of the LDL receptor is functionally conserved in man, monkey, cow, rabbit and guinea pig, but is quite distinct in rat, mouse and hamster.

Cholesterol stimulation of HDL binding to human endothelial cells EAhy 926 and skin fibroblasts: evidence for a mechanism independent of cellular metabolism.

The properties of the HDL binding site on the permanent human cell line EAhy 926 were studied. This cell line presents with highly differentiated functions of vascular endothelium. EAhy 926 cells possess HDL3 saturable binding sites with a Kd of about 20 micrograms/ml, which were up-regulated by cholesterol and were pronase- and EDTA-insensitive. Furthermore, HDL3 promoted cholesterol efflux from EAhy 926 cells in a dose-dependent manner. Thus, the HDL-binding site in EAhy 926 cells is similar to that present in fibroblasts, smooth muscle cells and endothelial cells. Up-regulation of HDL binding by cholesterol did not require de novo synthesis of HDL 'receptor' protein, as shown by the lack of effect of cycloheximide and alpha-amanitin and also occurred in fixed, non-living cells. Similar results were obtained using human skin fibroblasts. From these data we conclude that: (a) EAhy 926 cells are a good model for studying the HDL interaction with endothelial cells; (b) a mechanism independent of cellular metabolism is involved in the cholesterol-mediated up-regulation of HDL binding sites in EAhy 926 cells and human skin fibroblasts.

Reduction of LDL production rate in ileal bypassed rabbits treated with lovastatin.

The effect of lovastatin on the low density lipoprotein metabolism in bypassed rabbits was investigated. Partial ileal bypass effectively reduced total and low density lipoprotein (LDL) cholesterol by 44 and 48% respectively. The LDL drop was due to an increased fractional catabolic rate (FCR) of apolipoprotein B (apo B) from 0.74 to 1.27 pools per day with no effect on the apo B absolute catabolic rate and an increased expression of liver LDL receptors (+71%). Association of lovastatin with PIB resulted in a further decrease of total and LDL cholesterol (56 and 75% respectively) as compared to bypassed animals, without effects on the LDL FCR (1.27 +/- 0.11 versus 1.42 +/- 0.13 pools/day) or the expression of LDL receptors by the liver. The reduction of LDL was due to a decrease of the apolipoprotein B absolute synthetic rate (8.5 +/- 1.7 versus 13.6 +/- 1.7 mg/day). From these data we conclude that in bypassed rabbits lovastatin lowers total and LDL cholesterol mainly by reducing apolipoprotein B production rate.

Assimilation of LDL by experimental tumours in mice.

We have studied the uptake of 125I-labelled low-density lipoprotein (LDL) by seven experimental murine tumours in vivo. Four tumours (Lewis Lung carcinoma, B-16, MS-2 and Colon 26) showed a higher relative uptake of lipoprotein as compared to the liver, two (L-1210 and P-388) had a very low lipoprotein uptake, while lipoprotein uptake by tumour M5 was similar to that of the liver. The data was confirmed by tracing tissue uptake of lipoproteins using [14C]sucrose-labeled LDL. These in vivo findings correlated well with the in vitro specific binding of 125I-beta-VLDL to membranes prepared from tumours, thus suggesting that the expression of the LDL receptor in the tumours is related to the in vivo uptake of lipoprotein. Further analysis of the LDL receptor by ligand blotting showed that the tumor receptor has several of the liver LDL receptor characteristics (including apparent Mr, sensitivity to proteinases, and Ca2+ requirement of lipoprotein binding). In summary, our data show that experimental murine tumours express the LDL receptor and suggest that the high relative in vivo uptake of LDL is determined by the elevated LDL-receptor expression in the tumours.

Plasma lipoproteins and cholesterol metabolism in spontaneously hyperlipemic rats.

The aim of this study was to characterize the plasma lipoprotein pattern and some aspects of cholesterol metabolism in a line of hyperlipemic male rats. Plasma cholesterol and triglycerides were increased about 3-fold as compared to control animals (238 vs. 75 and 185 vs. 59 mg/dl respectively). The plasma lipoprotein distribution and the chemical composition of the isolated lipoproteins was unaffected. Plasma triglyceride production rate was increased (40%, P less than 0.01) and post-heparin lipoprotein lipase activity in plasma decreased (-28%, P less than 0.01) in the hyperlipemic rat. The activity of 3 enzymes involved in cholesterol metabolism (HMG-CoA reductase, cholesterol 7 alpha-hydroxylase, and acyl-CoA cholesterol-acyltransferase) did not differ from control values. 3H2O incorporation into digitonin-precipitable sterols, however, was significantly higher than in controls. This finding was due, in part, to an increased liver weight in the hyperlipemic animals. Furthermore kinetic data using 125I-LDL showed that the fractional catabolic rate of lipoprotein was within the normal range, while the synthetic rate of LDL protein was increased (0.67 vs. 0.3 mg/kg/h, P less than 0.01) in the hyperlipemic rat. These observations suggest that multiple metabolic defects underline the hyperlipemia observed in this animal model.

Progesterone modulates the expression of HDL binding sites in human skin fibroblasts.

The aim of this work was to study the effects of progesterone on the expression of high density lipoprotein binding sites by cultured human skin fibroblasts. At concentrations ranging between 10(-6)- and 10(-4) M the hormone showed a dose-dependent induction of the HDL binding sites. The effect was maximal at 48 h. The increased HDL binding was only due to an up-regulation of binding sites, without changes of the apparent Kd. This effect was not related to changes of cellular cholesterol content, and was not affected by inhibition of protein synthesis. These data suggest that the expression of binding sites for HDL can be modulated via a mechanism that does not depend upon cellular cholesterol content.

A dot-blot assay for the low density lipoprotein receptor.

We describe a new method for detecting the interaction of low density lipoprotein with its receptor using unmodified nitrocellulose as support for membrane protein. The method is specific and sensitive down to 3 micrograms of membrane protein. Unlabeled LDL, but not HDL, competes with 125I-labeled LDL for binding, and binding is abolished by pretreatment of the membranes with pronase and is dependent upon the presence of Ca2+. Furthermore, modification of arginine or lysine residues on LDL abolishes the lipoprotein interaction with the receptor protein supported on the nitrocellulose. When the membranes are solubilized with octyl glucoside, purification steps of the receptor can be directly followed with no interference of the detergent, therefore eliminating the need for its removal. The increased expression of LDL receptors on liver membranes from estradiol-treated rats was also demonstrated. We suggest, therefore, that this method can be used to detect the presence of LDL receptors on minute amounts of membrane protein.

Cholesterol feeding to rats does not modulate the expression of binding sites for HDL on liver membranes.

The binding of HDL, Apo-E-free, was studied in rats fed a cholesterol rich diet for 2, 4 and 7 days. Plasma cholesterol increased up to 16-fold (from 55 to 900 mg/dl); liver cholesterol was also raised, from 0.5 to 16 mg/g of tissue. The HDL binding to membrane preparations was not affected while the binding of beta VLDL was reduced to about 50% of the controls. These data show, therefore, that liver binding sites for HDL are refractory to regulation by dietary cholesterol.

A saturable binding site for high density lipoprotein3 on human liver membranes.

The binding of High Density Lipoprotein3 (HDL) to human liver membranes obtained from male normolipemic subjects was studied. High Density Lipoprotein3 binds in a specific, saturable manner to liver membranes; furthermore, this binding site appears to be distinct from these previously described for Low Density Lipoprotein (LDL) and chylomicron remnants. Competition experiments using Apo A-I reconstituted lipoproteins suggest that Apo A-I could be the determinant of the binding.